Phenolic compounds are well known for their biological activity and, due to their
reactivity, are important starting materials for the synthesis of complex
molecules. These compounds can be obtained either by chemical synthesis or
by extraction from different biological media. Thus, solubility in aqueous
systems, organic and supercritical solvents are fundamental for a better design
of reaction, separation and purification processes involving these molecules.
For phenolics not many phase equilibria data are available. Usually, when data
are reported, only a limited range of thermodynamic conditions is presented,
and for many of the more complex phenolics data are extremely scarce or
unavailable.
In our laboratory we have been implementing a systematic study on the
solubility of different hydroxybenzoic, phenylpropenoic and more complex
phenolics in water and several organic solvents. Solubilities were determined
using the analytical shake-flask method for generating the saturated solutions,
followed by compositional analysis by Uv-vis spectrophotometry, HPLC and/or
gravimetry [1,2]. A synthetic method based on the use of differential scanning
calorimetry (DSC) for determining solubilities has also been investigated.
For better understanding the solubilization process, melting properties (Tfus and
DfusH) were determined by DSC and aqueous acid dissociation constants by
potentiometric titration [1, 2].
Modeling was performed with the Cubic-plus-Association (CPA) equation of
state, where a predictive methodology for obtaining the pure component
parameters solely from the chemical structure is proposed. In this, the cubic
parameters are obtained from correlations involving Tc, Pc and the van der
Waals volume, while the association term parameters depend on the nature and
position of each associating group [1,2].
Results showed that a good description of the solubility of phenolics using a
single, small and temperature independent binary interaction parameter can be
obtained in different solvents.